Surely you mean nitrogen, the reason for using nitrogen is that it does not expand with heat, thereby maintaining a constant pressure, also noitrogen molecules are larger than regular air meaning that it will take longer for the tyre to deflate (yes they do that all the time as the molecules seep through the tyre very slowly) also pure nitrogen does not contain water molecules which can corrode the valve or freeze in extreme temps causing imbalance.
Realistically the amount of ice which would form in a vehicle tyre would be so small as to have no more effect than a small stone stuck in the tread. Corrosion of the valve would take longer than wearing out the tyres & leakage is so slow that it is negligable, also once you have filled with nitrogen you must always top up with it in order to maintain the advantage. Did they remove all the air from the tyre first? If not you just have tyres filled with air containing a larger % nitrogen.
Now why would you fill a tyre with nitrous, a gas used to enhance the performance of an engine, a gas which from experience changes pressure considerably with the application of heat?